Optical recording, producing apparatus, and method with peak-hold voltage features

ABSTRACT

The present invention proposes a method of controlling the laser power of a semiconductor laser that, in this method of controlling the laser power of a semiconductor laser by applying a power source voltage to between the collector and emitter of an output transistor and a serial circuit of the output transistor and a semiconductor laser, enables decreasing the power consumption of the output transistor. The present invention is arranged to apply a variable power source voltage Vcc to a serial circuit of an output transistor (Qb) and a semiconductor laser (SL) and thereby control the variable power source voltage Vcc such that a difference between the variable power source voltage Vcc and the peak hold voltage of an operating voltage of the semiconductor laser (SL) becomes substantially constant.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. patentapplication Ser. No. 10/169,734 filed on Dec. 12, 2002, which is basedupon and claims the benefit of priority from prior Japanese PatentApplication No 2000-351407 filed Nov. 17, 2000. The entire contents ofthe above-identified applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a laser power controlling method andapparatus for a semiconductor laser, and a recording/reproducing methodand apparatus for a magneto-optical recording medium, and arecording/reproducing method and apparatus for an optical recordingmedium.

2. Description of the Related Art

A conventional example of a semiconductor laser driving circuit will beexplained with reference to FIG. 6. In FIG. 6, SL designates ahigh-output purple color semiconductor laser [GaN-based semiconductorlaser (laser diode)] while DSL designates a drive circuit for drivingthe semiconductor laser SL. Hereinafter, a detailed explanation will nowbe given of the drive circuit for driving this semiconductor laser withreference to a timing chart of FIG. 7 as well. It is to be noted thatthe timing charts of FIG. 7 are illustrated considering a case where thesemiconductor laser SL is used in an optical head as later described ofthe optical disk recording/reproducing apparatus (recording/reproducingmethod).

This drive circuit DSL is constructed of a switch-equipped currentsource circuit SIK and an output transistor Qb. The switch-equippedcurrent source circuit SIK is constructed of a switch transistor (forexample, an NPN type transistor) Qa, a current source IS, and resistorsR₁₀, R₁₁ and R₁₂. The output transistor Qb is constructed of, forexample, a PNP type transistor.

The emitter of the transistor Qa is grounded, and the base thereof isgrounded via a base-biasing resistor R₁₁. The collector of thetransistor Qa is connected to a power source of Vcc=10V via the currentsource IS and the resistor R₁₀. A point of connection between thecurrent source IS and the resistor R₁₀ is connected to the base of thetransistor Qb. The emitter of the transistor Qb is connected to thepower source of Vcc=10V while the collector thereof is connected to theanode of the semiconductor laser (a laser diode) SL and the cathodethereof is grounded.

A control signal CS from an input terminal T2 is supplied to the base ofthe transistor Qa via the resistor R₁₂, whereby the transistor Qa ison/off controlled. As illustrated in FIG. 7C, this control signal CS, atthe time of recording, changes alternately to “1” and “0” and, at thetime of reproduction, is always kept to have a level of “1”. Also, apeak current setting signal CI is supplied to the current source IS froman input terminal T1 and, as illustrated in FIG. 7B, a control isperformed such that the peak current Ip at the time of recording becomeslarger in amount than the peak current Ip at the time of reproduction.Further, a Vop in each of FIGS. 6 and 7A represents the operatingvoltage of the semiconductor SL. An Iop in FIG. 6 represents theoperating current of the semiconductor laser SL.

The switching transistor Qa, at the time of reproduction, is always kept“on” and, at the time of recording, is turned on/off in correspondencewith the recording timing (or in correspondence with the recordingdata). Accordingly, at the time of reproduction, the operating voltageVop of the semiconductor laser SL has a constant voltage of, forexample, 5.5 V while, at the time of recording, that operating voltagebecomes a pulse voltage wherein a level of 7.0 V and a level ofapproximately OV are alternately repeated. The operating current Iop ofthe semiconductor laser SL, at the time of reproduction, has a constantvalue of, for example, 50 mA, and, at the time of recording, has anaverage current value of, for example, 110 mA.

Incidentally, although there is a case where, at the time ofreproduction, with an aim to decrease the noises, a small-amplitude sinewave signal of several hundreds of MHz is superimposed on the operatingcurrent lop of the semiconductor laser SL, but since this has no directrelevancy to the operation of the semiconductor laser driving circuitDSL, the illustration is omitted.

Although, in the semiconductor laser driving circuit DSL of FIG. 6, anNPN type transistor is used as the switching transistor Qa of theswitch-equipped current source circuit SIK and a PNP type transistor isused as the output transistor Qb, as illustrated in FIG. 8, a PNP typetransistor may be used as the switching transistor Qa and an NPN typetransistor may be used as the output transistor Qb.

The semiconductor laser driving circuit in that case will now beexplained with reference to FIG. 8. Incidentally, in FIG. 8, therelevant explanation will be made with the same reference symbols beingused to designate the corresponding portions to those of FIG. 6. Thisdrive circuit DSL is constructed of the switch-equipped current sourcecircuit SIK and the output transistor Qb. The switch-equipped currentsource circuit SIK is constructed of the switching transistor (PNP typetransistor) Qa, current source IS, and resistors R₁₀, R₁₁ and R₁₂. Theoutput transistor Qb is constructed of an NPN type transistor.

The emitter of the transistor Qa is connected to the power source ofVcc=10V, and the base thereof is connected to the power source ofVcc=10V via the base-biasing resistor R₁₁. The collector of thetransistor Qa is grounded via the current source IS and the resistorR₁₀. The connection point between the current source IS and the resistorR₁₀ is connected to the base of the transistor Qb. The emitter of thetransistor Qb is grounded while the collector thereof is connected tothe cathode of the semiconductor laser (a laser diode) SL and the anodethereof is connected to the power source of Vcc=10V.

From the input terminal T2 the control signal CS is supplied to the baseof the transistor Qa via the resistor R₁₂, whereby the transistor Qa ison/off controlled. This control signal CS, at the time of recording,changes alternately to “1” and “0” and at the time of reproduction, isalways kept to have a level of “0”. Further, from the input terminal T1the peak current setting signal CI is supplied to the current source ISand a control is performed such that the peak current Ip at the time ofrecording becomes larger in amount than the peak current Ip at the timeof reproduction. The Vop represents the operating voltage of thesemiconductor SL. The Iop represents the operating current of thesemiconductor laser SL.

For example, the drive circuit for driving the semiconductor laser inFIG. 6 will be described below. The power consumption P of the outputtransistor Qb is expressed by the following equation (1).P=(Vcc−Vop)×Iop  (1)

Calculating by substituting Vcc=V10V, Vop=5.5 V (minimum value), andIop=110 mA (maximum value) into the equation (1) above, the powerconsumption P of the output transistor Qb is expressed as done by thefollowing equation (2).P=(10−5.5)V×110 mA=495 mW  (2)

For example, in case of a red color semiconductor laser, calculating bysubstituting Vcc=5V, Vop=1.8 V (minimum value), and Iop=120 mA (maximumvalue) into the equation (1) above, the power consumption P of theoutput transistor Qb is expressed as done by the following equation (3).P=(5−1.8)V×110 mA=352 mA  (3)

Namely, the power consumption P of the output transistor Qb is smallcompared with the high-output purple semiconductor laser.

As apparent from the foregoing, since the power consumption of theoutput transistor Qb in the case where the high-output purplesemiconductor laser is used becomes fairly high compared with the powerconsumption of the output transistor Qb in the case where the red colorsemiconductor laser is used, it is necessary that a large-sized heatradiator should be attached to the output transistor Qb. However, sincethe drive circuit for the semiconductor laser is incorporated into theoptical head (optical pick-up) jointly with the semiconductor laser, ifproviding a radiator on the output transistor Qb, the optical head(optical pick-up) inconveniently becomes large in size. However, if alarge-sized radiator is not provided on the output transistor Qb, thisoutput transistor Qb generates heat, which shortens the service life ofthe optical head (optical pick-up) and that of the semiconductor laser.

In view of the above-described points in problem, the present inventionis intended to propose a laser power controlling method and apparatusfor a semiconductor laser, the method and apparatus being arranged tocontrol the laser power of a semiconductor laser by applying a powersource voltage to a serial circuit of a path between the collector andemitter of the output transistor and a semiconductor laser, in which thepower consumption of the output transistor can be decreased

Also, the present invention is intended to propose arecording/reproducing method for a magneto-optical recording medium, inwhich a convergent laser light based on a laser light from asemiconductor laser is irradiated onto a magneto-optical recordingmedium to heat the same; a magnetic field based on recording informationis applied to the heated portion of the magneto-optical recording mediumto thereby record the information into the heated portion thereof; and aconvergent laser light based on a laser light from the semiconductorlaser is irradiated onto the magneto-optical recording medium having theinformation recorded therein to thereby reproduce the information byusing the laser light emitted from the magneto-optical recording mediumhaving the information recorded therein, whereby a power source voltageis applied to a serial circuit of a path between the collector andemitter of the output transistor and a semiconductor laser to therebycontrol the laser power of the semiconductor laser, therecording/reproducing method thereby enabling decreasing the powerconsumption of the output transistor.

Further, the present invention is intended to propose arecording/reproducing apparatus for a magneto-optical recording mediumwhich includes an optical head that emits a convergent laser light basedon a laser light from a semiconductor laser and magnetic field generatormeans that applies a magnetic field based on recording information to amagneto-optical recording medium; the convergent laser light from theoptical head is irradiated onto the magneto-optical recording medium toheat the same and the magnetic field from the magnetic field generatormeans is applied to the heated portion of the magneto-optical recordingmedium to thereby record the information; and a convergent laser lightfrom the optical head is irradiated onto the magneto-optical recordingmedium having the information recorded therein to thereby obtain fromthe optical head a reproduction information signal based on an emittedlaser light from the magneto-optical recording medium having theinformation recorded therein, whereby a power source voltage is appliedto a serial circuit of a portion between the collector and emitter of anoutput transistor and the semiconductor laser to thereby control thelaser power of the semiconductor laser, thereby enabling decreasing thepower consumption of the output transistor.

Further, the present invention is intended to propose arecording/reproducing method for an optical recording medium, in which aconvergent laser light, based on a laser light from a semiconductorlaser, which is optically modulated by information is irradiated onto anoptical recording medium to thereby record the information; a convergentlaser light based on a laser light from the semiconductor laser isirradiated onto the optical recording medium having the infonnationrecorded therein to thereby reproduce the information in accordance withan emitted laser light from the optical recording medium having theinformation recorded therein, whereby a power source voltage is appliedto a serial circuit of a portion between the collector and emitter of anoutput transistor and the semiconductor laser to thereby control thelaser power of the semiconductor laser, thereby enabling decreasing thepower consumption of the output transistor.

Further, the present invention is intended to propose arecording/reproducing apparatus for an optical recording medium whichincludes an optical head that emits a convergent laser light, based on alaser light from a semiconductor laser, which is optically modulated byinformation and a convergent laser light which is not opticallymodulated by information, whereby, by irradiating onto an opticalrecording medium the convergent laser light of the laser light opticallymodulated by information from the optical head, the information isrecorded and, by irradiating onto the information-recorded opticalrecording medium the convergent laser light which is not opticallymodulated by information from the optical head, a reproductioninformation signal based on the laser light from theinformation-recorded optical recording medium is obtained from theoptical head, to thereby control the laser power of the semiconductorlaser, thereby enabling decreasing the power consumption of the outputtransistor.

SUMMARY OF THE INVENTION

A first invention provides a laser power controlling method for asemiconductor laser, which is arranged to include a step of applying avariable power source voltage to a serial circuit of an outputtransistor and a semiconductor laser; and a step of controlling thevariable power source voltage such that a difference between thevariable power source voltage and the peak hold voltage of an operatingvoltage of the semiconductor laser becomes substantially constant.

A second invention provides a laser power controlling device for asemiconductor laser, which includes a serial circuit of an outputtransistor and a semiconductor laser; a variable power source devicethat applies a variable power source voltage to the serial circuit; apeak hold circuit that obtains the peak hold voltage of an operatingvoltage of the semiconductor laser; and control means that controls thevariable power source device such that a difference voltage between thevariable power source voltage and the peak hold voltage becomes asubstantially constant voltage.

A third invention provides a recording/reproducing method for amagneto-optical recording medium, in which a convergent laser lightbased on a laser light from a semiconductor laser is irradiated onto amagneto-optical recording medium to heat the same; a magnetic fieldbased on recording information is applied to the heated portion of themagneto-optical recording medium to thereby record the recordinginformation into the heated portion thereof; and a convergent laserlight based on a laser light from the semiconductor laser is irradiatedonto the magneto-optical recording medium having the informationrecorded therein to thereby reproduce the information by using the laserlight emitted from the magneto-optical recording medium having theinformation recorded therein, whereby a variable power source voltage isapplied to a serial circuit of an output transistor and a semiconductorlaser; and the variable power source voltage is controlled such that adifference voltage between the variable power source voltage and thepeak hold voltage becomes a substantially constant voltage.

A fourth invention provides a recording/reproducing apparatus for amagneto-optical recording medium which includes an optical head thatemits a convergent laser light based on a laser light from asemiconductor laser and magnetic field generator means that applies amagnetic field based on recording information to a magneto-opticalrecording medium, whereby the convergent laser light from the opticalhead is irradiated onto the magneto-optical recording medium to heat thesame and the magnetic field from the magnetic field generator means isapplied to the heated portion of the magneto-optical recording medium tothereby record the information; and a convergent laser light from theoptical head is irradiated onto the magneto-optical recording mediumhaving the information recorded therein to thereby obtain from theoptical head a reproduction information signal based on an emitted laserlight from the magneto-optical recording medium having the informationrecorded therein, whereby the apparatus includes a serial circuit of anoutput transistor and a semiconductor laser; a variable power sourcedevice that applies a variable power source voltage to the serialcircuit; a peak hold circuit that obtains the peak hold voltage of anoperating voltage of the semiconductor laser; and control means thatcontrols the variable power source device such that a difference voltagebetween the variable power source voltage and the peak hold voltagebecomes a substantially constant voltage.

A fifth invention provides a recording/reproducing method for an opticalrecording medium, in which a convergent laser light, based on a laserlight from a semiconductor laser, which is optically modulated byinformation is irradiated onto an optical recording medium to therebyrecord the information; and a convergent laser light based on a laserlight from the semiconductor laser is irradiated onto the opticalrecording medium having the information recorded therein to therebyreproduce the information in accordance with an emitted laser light fromthe optical recording medium having the information recorded therein,whereby a variable power source voltage is applied to a serial circuitof an output transistor and a semiconductor laser; and the variablepower source voltage is controlled such that a difference voltagebetween the variable power source voltage and the peak hold voltagebecomes a substantially constant voltage.

A sixth invention provides a recording/reproducing apparatus for anoptical recording medium which includes an optical head that emits aconvergent laser light, based on a laser light from a semiconductorlaser, which is optically modulated by information and a convergentlaser light which is not optically modulated by information, whereby, byirradiating onto an optical recording medium the convergent laser lightof the laser light optically modulated by information from the opticalhead, the information is recorded and, by irradiating onto theinformation-recorded optical recording medium the convergent laser lightwhich is not optically modulated by information from the optical head, areproduction information signal based on the laser light emitted fromthe information-recorded optical recording medium is obtained by theoptical head, whereby the apparatus includes a serial circuit of anoutput transistor and a semiconductor laser; a variable power sourcedevice that applies a variable power source voltage to the serialcircuit; a peak hold circuit that obtains, the peak hold voltage of anoperating voltage of the semiconductor laser; and control means thatcontrols the variable power source device such that a difference voltagebetween the variable power source voltage and the peak hold voltagebecomes a substantially constant voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a recording/reproducing apparatusfor a magneto-optical disc according to an embodiment of the presentinvention;

FIG. 2 is a circuit diagram illustrating an example of a laser powercontrol circuit for a semiconductor laser according to the embodiment ofthe present invention;

FIG. 3 is a diagram illustrating the voltages and waveforms atrespective portions in the laser power control circuit for thesemiconductor laser according to the embodiment of the presentinvention;

FIG. 4 is a circuit diagram illustrating another example of the laserpower control circuit for the semiconductor laser according to theembodiment of the present invention;

FIG. 5 is a circuit diagram illustrating further example of the laserpower control circuit for the semiconductor laser according to theembodiment of the present invention;

FIG. 6 is a circuit diagram illustrating a prior art example of a drivecircuit for the semiconductor laser;

FIG. 7 is a timing chart of the prior art example of the drive circuitfor the semiconductor laser; and

FIG. 8 is a circuit diagram illustrating another example of the priorart drive circuit for the semiconductor laser.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, an example of a recording/reproducing apparatus (recordingapparatus and reproducing apparatus) for a magneto-optical discaccording to an embodiment of the present invention, that has a laserpower control circuit for a semiconductor laser as later described willbe explained with reference to FIG. 1. In FIG. 1, a reference numeral 1denotes an magneto-optical disc, which is driven to rotate by a spindlemotor SM via a spindle. The spindle motor SM is servo controlled by aspindle motor servo circuit 2 . This servo circuit 2 is controlled by acontrol device (having a microcomputer built therein).

A reference numeral 3 denotes an optical head (optical pick-up) in whichthere is built in a semiconductor laser, the laser light from whichenters an objective lens via an optical system, and a convergent laserlight emitted therefrom is irradiated onto the recording surface of themagneto-optical disc 1. The optical head 3 is controlled by a focus andtracking servo circuit 4. The power of the laser light from thesemiconductor laser is controlled by a laser power control circuit 6according to a recording/reproducing laser power setting control signalfrom the control device 8.

A reference numeral 5 denotes an electromagnet, which is disposed on aside that is opposite, with respect to the magneto-optical disc 1, tothe side where the objective lens is located, and which is driven by anelectromagnet driving circuit 11. At the time of recording, therecording surface of the magneto-optical disc 1 is heated by theconvergent laser light up to the Curie point or more. Thereafter, to theportion whose temperature has decreased there is applied by theelectromagnet 5 a magnetic field whose polarities correspond to “1” and“0” of the recording data, whereby the recording data is recorded ontothe recording surface of the magneto-optical disc 1. The recording datafrom an input terminal 9 a is supplied to an ECC addition circuit 9,whereby the ECC (Error Correction Code) is added to the recording data.Thereafter, this recording data is supplied to a modulator circuit 10where it is digital-modulated. And this modulated recording data issupplied to the electromagnet driving circuit 11. Also, this modulatedrecording data from the modulator circuit 10 is supplied to the laserpower control circuit 6 as well.

When reproducing from the optical head 3, a weak laser light forreproduction is irradiated onto the recording surface of themagneto-optical disc 1. The reflected light returns to the optical head3, whereby a MO (magneto-optical) RF (radio frequency) signal and a PIT(pit) (high intensity light) RF signal are outputted. The MO RF signalis supplied to an RF binarizing circuit 13, thereby a binary signal isobtained. This binary signal is supplied to a digital demodulatorcircuit 14 and is thereby demodulated. This demodulated digital signalis supplied to an ECC decoder circuit 15, thereby error correctionprocessing is executed. This error-corrected reproduction data is outputto an output terminal 15 a. The PIT RF signal from the optical head 3 issupplied to a header information decoder circuit 7 and is therebydecoded. And the header information data thus obtained is supplied tothe control device 8.

In the recording/reproducing apparatus of FIG. 1, when a phase changetype optical disc or an optical disc using a pigment is adopted in placeof the magneto-optical disc 1, the apparatus may be constructed in theway of omitting the electromagnet 5 and electromagnet driving circuit11, supplying the modulated recording data from the modulator circuit 10directly to the laser power control circuit 6, and making the operatingvoltage of the semiconductor laser on or off in correspondence with thatrecording data.

Hereinafter an example of the laser power control apparatus for thesemiconductor laser according to the embodiment of the present inventionwill be explained in detail with reference to FIG. 2. It is to be notedthat, in FIG. 2, the portions corresponding to those in FIG. 6 aredenoted by the same reference symbols. A symbol DSL denotes a drivecircuit for a semiconductor laser, which is constructed of aswitch-equipped current source circuit SIK and an output transistor Qbwhich are the same circuit construction as that explained in connectionwith FIG. 6. And, as in FIG. 6, the collector of the output transistorQb is connected to the anode of a semiconductor laser SL built in theoptical head 3 in FIG. 1, the cathode of which is grounded. Here,although the semiconductor laser SL is a GaN-based high output purplecolor semiconductor laser (a high output purple color laser diode), theinvention is not limited thereto.

A symbol PS denotes a DC-DC converter serving as a variable power sourcedevice whose output power source voltage can be varied. The power sourcedevice PS is grounded and, in addition, its variable power sourcevoltage Vcc is applied to a serial circuit of the output transistor Qband the semiconductor laser SL and is also applied to theswitch-equipped current source circuit SIK.

The operating voltage Vop of the semiconductor laser SL is applied to apeak hold circuit PH and is peak-held. This peak hold circuit PH isconstructed of an NPN type transistor Qc functioning as a diode and ahold capacitor C1. To the collector of the transistor Qc there isapplied the variable power source voltage Vcc from the power sourcedevice PS. The base of the transistor Qc is connected to the collectorof the output transistor Qb. The emitter of the transistor Qc isgrounded, via the hold capacitor C1.

By peak-holding the operating voltage Vop using this peak hold circuitPH, when the semiconductor laser SL has generated a pulse light, sincethe power source voltage Vcc instantly responds to the operating voltageVop, the switch-equipped current source circuit SIK can flow a necessarycurrent to the output transistor Qb.

The variable power source voltage Vcc of the power source device PS andthe peak-hold voltage (referred to as “Vh”) of the peak hold circuit PHhave their voltages divided by a resistance voltage divider of a serialcircuit of resistors R1 and R2 and by a resistance voltage divider of aserial circuit of resistors R3 and R4, respectively, in the same ratio.The respective divided voltage outputs are supplied, respectively, totheir corresponding A/D converters “b” and “c” of a microcomputer MC.Representing the resistance values of the resistors R1 to R4 by the samesymbols R1 to R4, the following relationship of equation (4) holds trueamong those resistance values.R1/(R1+R2)=R3/(R3+R4)  (4)

Rewriting this equation (4) for rearrangement, the following equation(5) results.R1/R2=R3/R4  (5)

The microcomputer MC includes, other than the above-described A/Dconverters “b” and “c”, a CPU “a”, a ROM “d” and RAM “e” respectivelyconnected to the CPU “a”, and a D/A converter “f” for performing D/Aconversion on a digital control signal from the CPU “a”.

This microcomputer MC operates in accordance with the program stored inthe ROM “d”. Namely, as illustrated in FIG. 3, it outputs from the D/Aconverter “f” an analog control signal (this maybe an instructionsignal, a PWM signal, etc.) permitting the difference voltage (Vcc−Vh)between the variable power source voltage Vcc of the power source devicePS and the peak hold voltage Vh of the peak hold circuit PH to become aconstant (substantially constant) voltage Vconst. It then supplies thatanalog signal to the power source device PS to thereby control thevariable power source voltage Vcc of the power source device PS.Incidentally, in FIG. 3, the symbol Vop represents the operating voltageof the semiconductor laser SL. This operating voltage Vop is the same asthat explained in connection with FIG. 7A when the semiconductor laserSL is a high output purple color semiconductor laser.

Regarding FIG. 2, a further explanation will be given. When recording, acontrol signal CS from an input terminal T3 is supplied to a D inputterminal of a D type flip-flop circuit D-FF. This control signal, asstated in conjunction with FIG. 7C, alternately changes to “1” and “0”in correspondence with the recording timing or recording data at thetime of recording and, when reproducing, is always kept to have a levelof “1”. A clock CLK, from an input terminal T4, for driving thesemiconductor laser is supplied to a clock inversion input terminal ofthe type flip-flop circuit D-FF. And a non-inverted output (pulse) ofthe D type flip-flop circuit D-FF is supplied, via the input terminalT2, to the base of a switching transistor of the switch-equipped currentsource circuit SIK.

When reproducing, a control signal CS at all times kept “1” is supplied,via the D type flip-flop circuit D-FF and via the input terminal T2, tothe base of the switching transistor of the switch-equipped currentsource circuit SIK. Also, the clock CLK from the input terminal T4 issupplied to a frequency divider FD and is frequency-divided with aprescribed frequency dividing ratio N (N is an integer two or more).This frequency-divided clock clk is supplied to the micro-computer MCand the power source device PS. As a result of the dividing operation,it is possible to more prevent the micro-computer MC, the digitalcalculator circuit within this micro-computer MC, and the clock CLK ofthe analog control signal (the instruction signal, PWM signal, etc.) ofthe micro-computer MC, from having their adverse effect upon thesemiconductor laser SL, and resultantly to decrease the entry of theclock CLK into the waveform of the light signal emitted from thesemiconductor laser SL.

Hereinafter, with reference to FIG. 4, another example of the laserpower control device for the semiconductor laser according to theembodiment of the present invention will be explained in detail,provided, however, that in FIG. 4 the portions corresponding to those inFIGS. 2 and 3 are denoted by the same reference symbols; and a relevantpartial explanation will be omitted. In this example, in place of themicro-computer MC of FIG. 2, a subtractor circuit SUB is used and, inplace of the power source device PS from which a variable voltage isobtained, there is used a power source device PS1 constructed of aboosting type DC-DC converter.

The subtractor circuit SUB is equipped with operational amplifiers OP1to OP3. The divided voltage from the resistance voltage divider circuitof resistors R1 and R2 is supplied to a non-inversion input terminal ofthe operational amplifier OP1 whose output terminal is connected to aninversion input terminal. And, the output voltage from the operationalamplifier OP1 is supplied, via a resistor R5, to a non-inversion inputterminal of the operational amplifier OP3, the output terminal andinversion input terminal of which are connected to each other through aresistor R8. The divided voltage from a resistance voltage dividercircuit of resistors R3 and R4 is supplied to a non-inversion inputterminal of the operational amplifier OP2 whose output terminal isconnected to its inversion input terminal. And, the output voltage ofthe operational amplifier OP2 is supplied, via a resistor P7, to theinversion input terminal of the operational amplifier OP3. Incidentally,when the resistance values of the resistors R1 to R8 are represented bythe symbols R1 to R8, these resistance values R1 to R8 are selected soas to satisfy the following relationship of equation (6).R1/R2=R3/R4, R5/R6=R7/R8  (6)

A power source device PS1 of the boosting type DC-DC converter isconstructed of a comparator “g” for comparing the output voltage fromthe operational amplifier OP3 of the subtractor circuit SUB with areference voltage of a reference voltage source “h”, NOR gates “i” and“j”, p-type MOS-FET “k”, and diode (m). The comparison output of thelevel comparator “g” is input to the NOR gate “j”; the clock clk fromthe frequency divider FD is input to the NOR gate “i”; the output of oneNOR gate “i” is input to the other NOR gate “j” while the output of theother NOR gate “j” is input to the one NOR gate “i”; and the output ofthe one NOR gate “i” is input to the gate of the pMOS-FET “k”. Thesource of the MOS-FET “k” is grounded and the drain thereof is connectedto the anode of the diode “m”, the variable power source voltage Vccfrom the cathode of which is applied to a serial circuit of the outputtransistor Qb and the semiconductor laser SL and also applied to theswitch-equipped current source circuit SIK.

And, as illustrated in FIG. 3, the subtractor output voltage from thesubtractor circuit SUB, which permits the difference voltage between thevariable power source voltage Vcc of the power source device PS1 and thepeak hold voltage Vh of the peak hold circuit to become constant(substantially constant) , is supplied to the level comparator “g” ofthe power source device PS1 to thereby control the variable power sourcevoltage Vcc of the power source device PS1.

Incidentally, in this example of FIG. 4, by inputting the clock clk fromthe frequency divider FD to the NOR gate of the power source device PSi,it is possible to decrease the entry or superimposing of the clock CLKfrom the power source device PSi into the waveform of the light signalfrom the semiconductor laser SL.

Hereinafter, with reference to FIG. 5, still another example of thelaser power control device for the semiconductor laser according to theembodiment of the present invention will be explained in detail,provided, however, that in FIG. 5 the portions corresponding to those inFIGS. 2, 3, and 4 are denoted by the same reference symbols; and arelevant partial complex explanation will be omitted. In this example,in place of the power source device PS1 comprised of the boosting typeDC-DC converter of FIG. 4, there is used a power source device PS2constructed of a series regulator.

The output voltage from the operational amplifier OP3 of the subtractorcircuit SUB similar to that in the example of FIG. 4 is supplied to thecomparator “g” for comparing this output voltage with the referencevoltage of the reference voltage source “h” of the power source devicePS2. This power source device PS2 is equipped, in addition to thereference voltage source “h” and comparator “g”, with, for example, anNPN type transistor “n”, whereby the comparison output of the comparator“g” is supplied to the base of the transistor “n”. And, to the collectorof the transistor “n”, there is applied a fixed level of direct currentvoltage (reference voltage) (for example, +10V) from the direct currentpower source DS. And, by the comparison output from the level comparator“g”, the impedance between the collector and emitter of the transistor“n” is controlled.

Namely, the subtractor output from the subtractor circuit SUB, whichpermits the difference voltage (Vcc−-Vh) between the variable powersource voltage Vcc of the power source device PS2 and the peak holdvoltage Vh of the peak hold circuit PH to become a constant(substantially constant) voltage Vconst, is supplied to the power sourcedevice PS2 to thereby control the variable power source voltage Vcc ofthe power source device PS2.

In case of FIG. 5, the control signal CS from the input terminal T2 issupplied directly to the switch-equipped current circuit SIK.

In this example of the laser power control circuit for the semiconductorlaser in FIG. 5, the power consumption is shared by the outputtransistor Qb and the transistor “n” of the power source device PS2.

According to the first invention, since it has been arranged to apply avariable power source voltage to a serial circuit of an outputtransistor and a semiconductor laser and to control the variable powersource voltage such that a difference between the variable power sourcevoltage and the peak hold voltage of an operating voltage of thesemiconductor laser becomes substantially constant, it is possible toobtain a laser power controlling method for a semiconductor laser thatenables decreasing the power consumption of the output transistor.

According to the second invention, since it has a serial circuit of anoutput transistor and a semiconductor laser, a variable power sourcedevice that applies a variable power source voltage to the serialcircuit, a peak hold circuit that obtains the peak hold voltage of anoperating voltage of the semiconductor laser, and control means thatcontrols the variable power source device such that a difference voltagebetween the variable power source voltage and the peak hold voltagebecome a substantially constant voltage, it is possible to obtain adevice for controlling the laser power of the semiconductor laser thatenables decreasing the power consumption of the output transistor.

According to the third invention, since it has been arranged, in arecording/reproducing method for a magneto-optical recording mediumwherein a convergent laser light based on a laser light from asemiconductor laser is irradiated onto a magneto-optical recordingmedium to heat the same; a magnetic field based on recording informationis applied to the heated portion of the magneto-optical recording mediumto thereby record the recording information into the heated portionthereof; and a convergent laser light based on a laser light from thesemiconductor laser is irradiated onto the magneto-optical recordingmedium having the information recorded therein to thereby reproduce theinformation by using the laser light emitted from the magneto-opticalrecording medium having the information recorded therein, such that avariable power source voltage be applied to a serial circuit of anoutput transistor and a semiconductor laser; and the variable powersource voltage be controlled such that a difference voltage between thevariable power source voltage and the peak hold voltage become asubstantially constant voltage, therefore it is possible to obtain arecording/reproducing method for a magneto-optical recording medium thatenables decreasing the power consumption of the output transistor.

According to the fourth invention, since it has been arranged, in arecording/reproducing apparatus for a magneto-optical recording mediumwhich includes an optical head that emits a convergent laser light basedon a laser light from a semiconductor laser and magnetic field generatormeans that applies a magnetic field based on recording information to amagneto-optical recording medium, whereby the convergent laser lightfrom the optical head is radiated onto the magneto-optical recordingmedium to heat the same and the magnetic field from the magnetic fieldgenerator means is applied to the heated portion of the magneto-opticalrecording medium to thereby record the information; and a convergentlaser light from the optical head is radiated onto the magneto-opticalrecording medium having the information recorded therein to therebyobtain from the optical head a reproduction information signal based onan emitted laser light from the magneto-optical recording medium havingthe information recorded therein, such that the apparatus includes aserial circuit of an output transistor and a semiconductor laser; avariable power source device that applies a variable power sourcevoltage to the serial circuit; a peak hold circuit that obtains the peakhold voltage of an operating voltage of the semiconductor laser; andcontrol means that controls the variable power source device such that adifference voltage between the variable power source voltage and thepeak hold voltage become a substantially constant voltage, therefore itis possible to obtain a recording/reproducing apparatus for amagneto-optical recording medium that enables decreasing the powerconsumption of the output transistor.

According to the fifth invention, since it has been arranged, in arecording/reproducing method for an optical recording medium in which aconvergent laser light, based on a laser light from a semiconductorlaser, which is optically modulated by information is irradiated onto anoptical recording medium to thereby record the information; and aconvergent laser light based on a laser light from the semiconductorlaser is irradiated onto the optical recording medium having theinformation recorded therein to thereby reproduce the information inaccordance with an emitted laser light from the optical recording mediumhaving the information recorded therein, such that a variable powersource voltage be applied to a serial circuit of an output transistorand a semiconductor laser; and the variable power source voltage becontrolled such that a difference between the variable power sourcevoltage and the peak hold voltage become a substantially constantvoltage, therefore it is possible to obtain a recording/reproducingmethod for an optical recording medium that enables decreasing the powerconsumption of the output transistor.

According to the sixth invention, since it has been arranged, in arecording/reproducing apparatus for an optical recording medium whichincludes an optical head that emits a convergent laser light, based on alaser light from a semiconductor laser, which is optically modulated byinformation and a convergent laser light which is not opticallymodulated by information, whereby, by irradiating onto an opticalrecording medium the convergent laser light of the laser light opticallymodulated by the information from the optical head, the information isrecorded and, by irradiating onto the information-recorded opticalrecording medium the convergent laser light which is not opticallymodulated by information from the optical head, a reproductioninformation signal based on the laser light emitted from theinformation-recorded optical recording medium is obtained from theoptical head, such that the apparatus includes a serial circuit of anoutput transistor and a semiconductor laser; a variable power sourcedevice that applies a variable power source voltage to the serialcircuit; a peak hold circuit that obtains the peak hold voltage of anoperating voltage of the semiconductor laser; and control means thatcontrols the variable power source device such that a difference voltagebetween the variable power source voltage and the peak hold voltagebecome a substantially constant voltage, therefore it is possible toobtain a recording/reproducing apparatus for an optical recording mediumthat enables decreasing the power consumption of the output transistor.

According to the first to the sixth inventions, since it is possible todecrease the power consumption of the output transistor, a radiator forthe output transistor becomes unnecessary. Even when such radiator isnecessary, it is sufficient to use a small-sized one.

According to the first to the sixth inventions, since it is possible todecrease the power consumption of the output transistor and thereforesince the rise in the temperature of the semiconductor laser and thelaser power control circuit disposed near that semiconductor laser canbe decreased, it is possible to prevent the defective operation and thedecrease in the service life of the semiconductor laser, the opticalhead, and the laser power control circuit. Further, considering aboutthe limitation of the temperature rise of the apparatus having theseoperational members loaded therein, miniaturization of the apparatusbecomes possible even if the size thereof must be selected greater thana predetermined size.

In general, while the operational voltage of the semiconductor laserincreases during its aged operation and the operational voltage comesnear to the power source voltage for the output transistor of the laserpower control circuit for the semiconductor laser and this leads to theend of the service life, according to the first to the sixth inventionsit is possible to make that power source voltage higher than that in theprior art, which enables extending the life of the semiconductor laser.

In the first to the sixth inventions, the effect of decreasing the powerconsumption of the output transistor becomes remarkable when thesemiconductor laser is a high output purple color semiconductor laser.

1. A laser power controlling method for a semiconductor laser,comprising: applying a variable power source voltage to a serial circuitof an output transistor and a semiconductor laser; monitoring anoperating voltage of the semiconductor laser; and controlling thevariable power source voltage such that a difference between thevariable power source voltage and a peak hold voltage of the operatingvoltage of the semiconductor laser become substantially constant.
 2. Thelaser power controlling method for a semiconductor laser according toclaim 1, wherein said semiconductor laser is a high-output purple colorsemiconductor laser.
 3. The laser power controlling method for asemiconductor laser according to claim 1, wherein the monitoring stepcomprises: obtaining the peak hold voltage of the operating voltage ofthe semiconductor laser.
 4. A laser power controlling device for asemiconductor laser, comprising: a serial circuit of an outputtransistor and a semiconductor laser; a variable power source thatapplies a variable power source voltage to the serial circuit; amonitoring circuit that monitors an operating voltage of thesemiconductor laser; and control means that controls the variable powersource device such that a difference voltage between the variable powersource voltage and a peak hold voltage of the operating voltage of thesemiconductor laser become a substantially constant voltage.
 5. Thelaser power controlling device for a semiconductor laser according toclaim 4, wherein said control means is a micro-computer.
 6. The laserpower controlling device for a semiconductor laser according to claim 4,wherein said control means is a subtraction circuit that subtracts thepeak hold voltage of said peak hold circuit from the variable powersource voltage of said variable power source device.
 7. The laser powercontrolling device for a semiconductor laser according to claim 4,wherein said variable power source device is a DC-DC converter.
 8. Thelaser power controlling device for a semiconductor laser according toclaim 4, wherein said variable power source device is a boosting typeDC-DC converter.
 9. The laser power controlling device for asemiconductor laser according to claim 4, wherein said variable powersource device is a series regulator.
 10. The laser power controllingdevice for a semiconductor laser according to claim 4, wherein saidsemiconductor laser is a high-output purple color semiconductor laser.11. The laser power controlling device for a semiconductor laseraccording to claim 4, wherein the monitoring circuit obtains the peakhold voltage of the operating voltage of the semiconductor laser.
 12. Arecording/reproducing method for an optical recording medium, in which aconvergent laser light, based on a laser light from a semiconductorlaser, which is optically modulated by information is irradiated onto anoptical recording medium to thereby record the information; a convergentlaser light based on a laser light from the semiconductor laser isirradiated onto the optical recording medium having the informationrecorded therein to thereby reproduce the information in accordance withan emitted laser light from the optical recording medium having theinformation recorded therein, comprising the steps of: applying avariable power source voltage to a serial circuit of an outputtransistor and the semiconductor laser; monitoring an operating voltageof the semiconductor laser; and controlling the variable power sourcevoltage such that a difference between the variable power source voltageand a peak hold voltage of the operating voltage of the semiconductorlaser become substantially constant.
 13. The recording/reproducingmethod for an optical recording medium according to claim 12, whereinsaid semiconductor laser is a high-output purple color semiconductorlaser.
 14. The recording/reproducing method for an optical recordingmedium according to claim 12, wherein the monitoring step comprises:obtaining the peak hold voltage of the operating voltage of thesemiconductor laser.
 15. A recording/reproducing apparatus for anoptical recording medium which includes an optical head that emits aconvergent laser light, based on a laser light from a semiconductorlaser, which is optically modulated by information and a convergentlaser light which is not optically modulated by information, whereby, byirradiating onto an optical recording medium the convergent laser lightof the laser light optically modulated by information from the opticalhead, the information is recorded and, by irradiating onto theinformation-recorded optical recording medium the convergent laser lightwhich is not optically modulated by information from the optical head, areproduction information signal based on the laser light emitted fromthe information-recorded optical recording medium is obtained by theoptical head, comprising: a serial circuit of an output transistor andthe semiconductor laser; a variable power source that applies a variablepower source voltage to the serial circuit; a monitoring circuit thatmonitors an operating voltage of the semiconductor laser; and controlmeans that controls the variable power source device such that adifference voltage between the variable power source voltage and a peakhold voltage of the operating voltage of the semiconductor laser becomea substantially constant voltage.
 16. The recording/reproducing methodfor an optical recording medium according to claim 15, wherein thecontrol voltage of said driving circuit for driving the semiconductorlaser, at the time of recording, is a pulse voltage having one certainamplitude voltage and, at the time of reproduction, is another certainconstant voltage lower in amplitude than said one certain amplitudevoltage.
 17. The recording/reproducing apparatus for an opticalrecording medium according to claim 15, wherein the control voltage ofsaid driving circuit for driving the semiconductor laser, at the time ofrecording, is a pulse voltage having one certain amplitude voltage and,at the time of reproduction, is another certain constant voltage lowerin amplitude than said one certain amplitude voltage.
 18. Therecording/reproducing apparatus for an optical recording mediumaccording to claim 15, wherein said control means is a micro-computer.19. The recording/reproducing apparatus for an optical recording mediumaccording to claim 15, wherein said control means is a subtractioncircuit that subtracts the peak hold voltage of said peak hold circuitfrom the variable power source voltage of said variable power sourcedevice.
 20. The recording/reproducing apparatus for an optical recordingmedium according to claim 15, wherein said variable power source deviceis a DC-DC converter.
 21. The recording/reproducing apparatus for anoptical recording medium according to claim 15, wherein said variablepower source device is a boosting type DC-DC converter.
 22. Therecording/reproducing apparatus for an optical recording mediumaccording to claim 15, wherein said variable power source deviceincludes a series regulator.
 23. The recording/reproducing apparatus foran optical recording medium according to claim 15, wherein saidsemiconductor laser is a high-output purple color semiconductor laser.24. The recording/reproducing apparatus for an optical recording mediumaccording to claim 15, wherein the monitoring circuit obtains the peakhold voltage of the operating voltage of the semiconductor laser.